Method for insulating oil wells



United States Patent 3,386,512 METHOD FOR INSULATING OIL WELLS Dolores Floyd Bloom, Bakersfield, Calif., assignor, by mesne assignments, to Big Three Industrial Gas & Equipment Co., a corporation of Texas Filed Sept. 24, 1965, Ser. No. 489,996 5 Claims. (Cl. 166-40) ABSTRACT OF THE DISCLOSURE The disclosure is of processes and apparatuses wherein insulation in Wells is created by maintenance of a layer or zone of an inert gas such as nitrogen. Maintenance of the insulation may be accomplished by moderate flows of the inert gas through the insulation zone. The insulation is maintained about a zone containing hot fluid within the well.

Brief summary of the invention In summary, the invention is to processes and apparatus for use in providing insulation in wells for preventing heat dissipation from fluids flowing into the wells, or out of the wells, for various heat treatments of materials in formattion around the wells, primarily for affecting their physical characteristics, including their flow characteristics. The insulation, in addition to minimization of heat losses, also serves to protect physical apparatus in the well and the well structure in general.

During the operation of some oil wells it has been found that oil components of very high viscosity tend to be retained in the base strata of the oil well rather than flow along and be removed with the lighter components. After the well has been in operation for an extended period of time, these slow moving oils of heavy viscosity are retained in the base strata and clog the strata pores thereby leading to an eventual decline in profitable production of the well.

It is a common practice in the oil industry following the decline of such an oil well to attempt a regeneration process by heating the oil bearing strata underlying the well and thereby reducing the viscosity of the heavy oils in order to unplug the strata. This may be accomplished by steam heating which lowers the viscosity of the oils and permits their removal from the pores of the strata; this allows additional oil to enter the well through the unplugged strata and extends the wells production life. The results of heat treatments are varied, but although they may extend the life of the oil well by as much as fifty percent, all the present treatments have one drawback in common, namely, their inability to provide efficient and suflicient heat transfer from the heating media to the oil strata. Consequently, the productive potential of many Wells cannot be realized and in even those cases where regeneration has been successful, a further improvement could be attained.

Another drawback of heat treating processes presently employed is that an undesirable thermal expansion of the metallic well casing occurs because of the excessive heating temperatures employed and this in many instances produces permanent distortion and in some cases even a fracturing of the casing.

Still another problem associated with heat distortion of the casing involves the use of packers during the heating operation. These packers are placed at the bottom of the well to seal off the central tubing or string from the casing and are positioned in the space between these two elements. If the packers become jammed in place due to heat distortion of the well casing, they can only be removed with difficulty if they can be removed at all.

It is therefore an object of this invention to provide an improved process for regenerating oil wells.

Another object of this invention is to minimize heat distortion in the metallic casing wall of an oil Well.

It is another object of this invention to improve the efficiency of prior art processes for supplying heat to the oil bearing strata of an oil well.

It is another object of this invention to eliminate the requirement of packers used in oil wells When heating the oil bearing strata of an oil well.

It is another object of this invention to insulate the outer metallic casing wall of an oil well from the heat of a heating medium in the central string.

It is another object of this invention to insulate the outer metallic casing of a thermal well from a hot fluid in the central string of the well.

It is a further object of this invention to provide an oil well structure having an insulating inert gas of low heat conductivity, such as nitrogen, between the outer metallic casing and the central tubing of the Well, the central tubing containing a hot fluid medium.

It is a still further object of this invention to provide a thermal well structure having an inert gas of low heat conductivity such as nitrogen insulating the space between the outer metallic casing and the central string of the well, the central string containing a hot fluid medium.

Other objects and advantages of the present invention will subsequently become more readily apparent upon reference to the following description and accompanying drawing.

In the drawing:

The single figure is an axial section of an oil well and adjacent formation including apparatus for performing the method of the present invention.

Referring more particularly to the drawing, an oil well 10 is shown having a casing wall 11 forming a space 12. The casing wall extends downwardly through a non-oil bearing formation 13 and terminates in an oil bearing strata 14 underlying the well. A central tubing or string 15 extends through the space 12 and into the strata. In normal operation, oil is pumped upwardly in the string from the oil bearing strata and is, of course, removed when it reaches the top of the string. A thick plate 16 is threaded into the casing wall at the top of the well at about ground level and functions as a seal. During regeneration of the well using a heating procedure, a fluid such as steam from a source not shown, is passed down the central string in the direction shown by the arrows. In the practice of the present invention, a conduit 17 is mounted in the plate 16 and connected to a source of nitrogen indicated as N The pressurizing system and apparatus for supplying the nitrogen to space 12 is quite conventional and is not here elaborated upon.

The objects of this invention are attained by the discovery that problems associated with heat treatment of the base strata of oil wells with steam or by other means may be overcome by providing a suitable insulating media in the space between the well casing and the central tubing during the heat treatment. Steam is the preferred fluid used for the heat treatment but other fluids are employed in various specific situations. For example, hot oxygen is passed down the central tubing when the fire flooding method is used to heat treat an oil bearing strata. Basically, this insulation medium comprises an inert, low heat conductive gas such as nitrogen which is filled into this space prior to the heat treatment operation. Helium is also suitable but is much more expensive. Preferably, the insulating effect is maintained during the heat treatment by continually adding nitrogen to the space at a low flow rate. Nitrogen is preferred because of its low cost and since it possesses physical properties which includes low heat conductivity and a very low flash point temperature.

Operation The operation of the described embodiment of the subject invention is believed to be readily apparent and is briefly summarized at this point. The addition of nitrogen which is indicated as N on the drawing provides an insulating medium in the space 12 between the casing wall 11 and the central bore and is effected through conduit 17 passing through plate 16. It is convenient that the nitrogen is at ambient temperature when it enters the space. In a preferred embodiment of this invention, the nitrogen is supplied under an initial pressure of about 2,400 psi. from a container, not shown, until space 12 has been filled. Continued pressure is applied to force nitrogen out the bottom of the casing and maintain the remaining nitrogen under pressure in space 12. Obviously a deeper well will require more nitrogen and a higher pressurization. Following pressurization of the space with nitrogen, the steam heating of the oil strata 14 is commenced, and for this purpose, steam from a source, not shown, is fed down into the central string in the direction shown by the arrows until it contacts the oil strata. The purpose of pressurizing the space with nitrogen before rather than during steam heating is simply to avoid an unnecessary heat transfer occurring prior to insulation being established. This prevents a loss of steam B.t.u.s and possible distortion of the well casing.

During the steaming process some nitrogen usually escapes from space 12, so if the insulating effect is to be maintained, this nitrogen must be replenished. This may be done intermittently or continuously but the latter method is preferred since a heat build-up associated with and intermittent replenishment is not desirable because it may distort the well casing. Continuous replenishment of the nitrogen is eflected at much lower pressures compared to the initial pressures used to fill the space. Following the steaming process, the sources of steam and nitrogen are removed, the nitrogen supply conduit is closed, and the well is set up for recovering the oil which now flows out through the unplugged pores of the strata.

While no exact explanation is known for the effectiveness of the process of this invention, the net result of using the process compared with prior methods of simply heating has been ascertained. For example, in the Bakersfield, Calif., oil fields, yields have been increased from three barrels per day using conventional techniques of steam heating to one hundred barrels per day when employing the present invention. Further more, these yields have been obtained with less B.t.u.s and the attendant cost saving resulting from a descreased use of an expensive steam generator and personnel which could be employed for other purposes.

By employing this process, thermal distortion of the casing has been reduced to tolerable levels, and this permits the oil strata to he heat treated without destroying the entire well. It is thought that because the side wall of the well casing is metallic, it acts as a sink that absorbs heat from the steam in the central string. This heat absorption prevents the full effect of the steam being utilized in the oil strata and also distorts the casing wall. Using an insulator such as nitrogen, heat transfer to the metal casing wall is minimized and the major effect of the steam heat can be employed to act on the oil strata.

Furthermore, since the nitrogen pressure prevents the steam from entering into the space between the wall casing and central string, the need for employing packers has been eliminated.

The present method of nitrogen insulation obviously has application to industries other than oil where it is desired to insulate the outer casing of the well from the thermal effect of a hot medium contained in one or more tubes in the center of the well. Sulfur wells are a good example of such an application.

Although the invention has been herein shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In a well process wherein a hot fluid medium is conveyed through a central pipe string of a well and the well includes a well causing surrounding the central pipe string, an improved process for insulating around the central pipe string, comprising introducing a gas consisting essentially of inert gas into the upper end of the well casing and flowing said gas downwardly through the well casing around the full length of the central pipe string and commingling said gas at the lower end of the central pipe string with said hot fluid medium, the amount of said gas introduced into the upper end of the well casing being suflicient to prevent said hot fluid medium from entering the lower end of the well casing.

2. The process as set forth in claim 1, wherein said inert gas is gaseous nitrogen.

3. The process as set forth in claim 2, said gaseous nitrogen being at about ambient temperature when introduced into the upper end of the well casing.

4. The process as set forth in claim 2, said hot fluid medium comprising steam flowing downwardly through the central pipe string to an earth formation surrounding the well.

5. The process as set forth in claim 2, said hot fluid medium comprising heated oxygen flowing downwardly through the central pipe string for combustion with combustible materials in an earth formation surrounding the well.

References Cited UNITED STATES PATENTS 895,612 8/1908 Baker 166-57 1,413,197 4/1922 Swan 166-57 1,565,574 12/1925 Larsen 166-40 2,245,870 6/1941 Norman 166-41 X 2,839,141 6/1958 Walter 16611 2,858,891 11/1958 Moll et al. 166-11 2,876,838 3/1959 Williams 166-11 2,966,346 12/1960 I-Iuitt et al 299-4 3,080,919 3/1963 Harlan 166-39 3,126,960 3/1964 Woodward et al. 1 6639 3,145,772 8/1964 Huitt 166-11 X 3,159,216 12/1964 Reed et al. 166-11 3,221,813 12/1965 Closmann et al. 166-40 X 3,280,909 10/1966 Closmann et a1. 166-11 X 1,259,537 3/1918 Lucas at al 2995 OTHER REFERENCES Nowsco Advertisment: In Composite Catalog of Oil Field Equipment and Services, Houston, Tex., Gulf Pub. Co., 1962, vol. 3, pp. 3588 and 3589.

CHARLES E. OCONNELL, Primary Examiner.

ERNEST R. PURSER, Examiner.

I. A. CALVERT, Assistant Examiner. 

